Abstract: The changes in water and temperature are typical weathering factors for the deterioration of physical and mechanical properties of engineering rock. In this study, uniaxial compression tests, splitting tensile tests and angle-changed shear tests were carried out on red-sandstone specimens under different water contents and freeze-thaw (F-T) cycles. Experimental results showed that main mechanical parameters such as uniaxial compressive strength, deformation modulus, splitting tensile strength, cohesion and friction angle decreased with the increase of water content and freeze-thaw cycles, but the laws of reduction were different. It was found that the softening effect of water on rock was obvious, and the damaging effect of F-T cycles on rock was more significant. The microstructure of rock specimens was analysed by scanning electron microscopy (SEM) under different water contents and freezing-thawing cycles. During the processes of water absorption and freezing-thawing cycle, the water softening on red sandstone plays the dissolution and medium roles. Meanwhile, the effect of temperature change is reflected in the disharmony of thermal deformation and phase transformation. An attenuation model of mechanical properties of red sandstone under freezing-thawing cycles was developed, and the attenuation rate and half-life of each mechanical parameter were analysed accordingly. The research results provide significant guidance for rock engineering in the water environment and cold regions.

Key words: water-softening effect, freeze-thaw cycles, microstructure, hydro-thermal coupling, decay model